1. Technical Field
The present invention relates to electro-optical devices and electronic apparatuses.
2. Related Art
As a typical electro-optical device, a liquid crystal device is known. The liquid crystal device includes, for example, a liquid crystal panel and a backlight disposed opposite the liquid crystal panel to emit light.
The liquid crystal panel includes a pair of substrates and a liquid crystal disposed therebetween. The liquid crystal panel is provided with a pair of electrodes. The pair of electrodes applies a drive voltage to the liquid crystal to change the alignment and order of liquid crystal molecules. Then, light emitted from a backlight and passing through the liquid crystal is changed so that images can be displayed with grayscale levels.
The visibility of display of the liquid crystal device changes depending on the brightness around the liquid crystal device due to external light, such as sunlight. That is, as the brightness around the liquid crystal device increases, the difference between the brightness around the liquid crystal device and the brightness of the display area of the liquid crystal device decreases. Accordingly, the visibility of the display of the liquid crystal device deteriorates.
To overcome this drawback, a liquid crystal device including an optical sensor for detecting the illuminance of external light has been proposed (see, for example, JP-A-2005-121997).
In this liquid crystal device, the illuminance of external light is detected by the optical sensor, and the amount of light emitted from a backlight is controlled in accordance with the detected illuminance of the external light. Thus, the amount of light emitted from the backlight and supplied to a liquid crystal panel can be adjusted in accordance with the brightness around the liquid crystal device. As a result, the visibility of the display of the liquid crystal device can be improved.
The above-described optical sensor includes a first PIN diode for receiving external light and a second PIN diode which is shielded from external light. The first PIN diode outputs an electric signal in accordance with, not only the illuminance of external light, but also the temperature of the PIN diode. On the other hand, the second PIN diode, which is shielded from external light, outputs an electric signal in accordance with factors, such as the temperature of the PIN diode, other than the illuminance of external light.
The optical sensor determines the difference between the electric signal output from the first PIN diode and the electric signal output from the second PIN diode. Accordingly, the optical sensor eliminates factors, such as the temperature of the PIN diode, other than the illuminance of external light, from the electric signal output from the first PIN diode, and then outputs the electric signal reflecting only the illuminance of the external light. By determining the amount of received external light on the basis of the level of the electric signal, the illuminance of the external light can be detected with high precision.
As described above, in order to detect the illuminance of the external light with high precision, it is necessary that the second PIN diode output an electric signal with high precision in accordance with factors, such as the temperature of the PIN diode, other than the illuminance of the external light. Accordingly, the degree to which the second PIN diode is shielded from light should be increased to eliminate the influence of the illuminance of external light from the electric signal output from the second PIN diode. Thus, between a pair of substrates of the liquid crystal panel, a light-shielding film for shielding the second PIN diode from external light is formed on the substrate on which the external light is incident. This light-shielding film can stop the external light incident on the liquid crystal panel from directly reaching the second PIN diode.
The external light incident on the liquid crystal panel is sometimes diffused between the pair of substrates of the liquid crystal panel. The above-described light-shielding film, however, cannot stop the diffused external light from reaching the second PIN diode, which serves as a light-shielded sensor. This decreases the degree to which the second PIN diode is shielded from light. Accordingly, the precision of the illuminance of the external light to be detected is decreased.